PRACH-based proximity detection

ABSTRACT

Improvements to signaling procedures for use in physical random access channel (PRACH)-based proximity detection are disclosed. Signaling and signaling processes from a serving base station may trigger a more efficient and reliable transmission of PRACH from related user equipment (UE). At the dynamic power nodes (DPNs) monitoring for such PRACH-based proximity, features are disclosed which establish neighbor lists for more efficient management of detection and proximity activation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/758,644, entitled, “PRACH-BASED PROXIMITY DETECTION”,filed on Jan. 30, 2013, which is expressly incorporated by referenceherein in its entirety.

BACKGROUND

Field

Aspects of the present disclosure relate generally to wirelesscommunication systems, and more particularly, to physical random accesschannel (PRACH)-based proximity detection.

Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, and the like. These wireless networks may be multiple-accessnetworks capable of supporting multiple users by sharing the availablenetwork resources. Such networks, which are usually multiple accessnetworks, support communications for multiple users by sharing theavailable network resources. One example of such a network is theUniversal Terrestrial Radio Access Network (UTRAN). The UTRAN is theradio access network (RAN) defined as a part of the Universal MobileTelecommunications System (UMTS), a third generation (3G) mobile phonetechnology supported by the 3rd Generation Partnership Project (3GPP).Examples of multiple-access network formats include Code DivisionMultiple Access (CDMA) networks, Time Division Multiple Access (TDMA)networks, Frequency Division Multiple Access (FDMA) networks, OrthogonalFDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.

A wireless communication network may include a number of base stationsor node Bs that can support communication for a number of userequipments (UEs). A UE may communicate with a base station via downlinkand uplink. The downlink (or forward link) refers to the communicationlink from the base station to the UE, and the uplink (or reverse link)refers to the communication link from the UE to the base station.

A base station may transmit data and control information on the downlinkto a UE and/or may receive data and control information on the uplinkfrom the UE. On the downlink, a transmission from the base station mayencounter interference due to transmissions from neighbor base stationsor from other wireless radio frequency (RF) transmitters. On the uplink,a transmission from the UE may encounter interference from uplinktransmissions of other UEs communicating with the neighbor base stationsor from other wireless RF transmitters. This interference may degradeperformance on both the downlink and uplink.

As the demand for mobile broadband access continues to increase, thepossibilities of interference and congested networks grows with more UEsaccessing the long-range wireless communication networks and moreshort-range wireless systems being deployed in communities. Research anddevelopment continue to advance the UMTS technologies not only to meetthe growing demand for mobile broadband access, but to advance andenhance the user experience with mobile communications.

SUMMARY

Representative aspects of the present disclosure are directed toincreased efficiencies in physical random access channel (PRACH)handling in relation to PRACH-based proximity detection based onover-the-air tuning. In selected aspects, signaling from a serving basestation may trigger periodic PRACH signaling for a UE. In such aspects,the PRACH signals do not rely on a single, related PDCCH from theserving base station. The signaling from the serving base station mayalso include various settings that the UE may use when transmittingPRACH, such as a transmission power setting, periodicity, PRACHtransmission thresholds, signature sets, and the like. The triggeringsignal may also notify the UE to transmit PRACH signals while stilldecoding any received PDCCH transmissions.

Various additional aspects may provide for the serving base station todelay sending the PRACH response messages in order for the UE totransmit multiple PRACH signals using increasing transmission power.After a certain period or when the PRACH transmission power reaches aparticular level, the serving base station will send the PRACH responsemessage; thus, causing the UE to stop PRACH transmissions.

Additional aspects of the present disclosure may also provide for anydynamic power nodes (DPNs) to establish neighbor lists that include setsof base stations with root sequences that are routinely monitored duringproximity detection. The list may change when the DPN activates into afull-powered mode or may be semi-statically set in a network-wideassignment. Each base station in the neighbor set may be assigned withspecific thresholds, in which the threshold may correspond to theirregular or asymmetric footprint of the cell deployment. Thesethresholds may be pre-determined or dynamically optimized based onvarious measurements, loading conditions, network events, or the like.

Additional aspects of the disclosure provide for neighbor-specific PRACHconfigurations for serving cell determination. This aspect allows a DPNto identify the serving cell based suitable partitioning of PRACHresources and analyzing when or which one of the preambles is received.Preambles, PRACH resources, and timing may be coordinated via thebackhaul or predetermined by the network or equipment manufacturers.Once the DPN determines the serving base station, correspondingthresholds, such as noted above, may be applied.

Further aspects of the present disclosure are directed to a method ofwireless communication that includes transmitting, from a serving basestation, a signal to a mobile device served by the serving base station,wherein the signal triggers periodic PRACH transmission from the mobiledevice.

Further aspects of the present disclosure are directed to a method ofwireless communication that includes receiving, at a mobile device, asignal from a serving base station and sending periodic PRACHtransmissions from the mobile device in response to the signal.

Further aspects of the present disclosure are directed to a method ofwireless communication that include entering a reduced power mode at aDPN, monitoring, by the DPN, for PRACH transmissions from one or moreUEs proximate to the DPN, detecting a plurality of candidate PRACHtransmissions, combining the plurality of candidate PRACH transmissionsat the DPN to determine a detected PRACH transmission from a UE,determining, by the DPN, a proximity of the UE based on the detectedPRACH transmission, and modifying operation of the DPN in response tothe proximity.

Further aspects of the present disclosure are directed to a method ofwireless communication that includes receiving, at a serving basestation, a PRACH transmission from a mobile device and delaying, by theserving base station, transmission of a PRACH acknowledgement message tothe mobile device.

Further aspects of the present disclosure are directed to a method ofwireless communication that includes entering a reduced power mode at aDPN, monitoring, by the DPN, for a set of root sequences associated withat least one base station in a neighbor list at the DPN, wherein the setof root sequences are located in PRACH transmissions from one or moreUEs, determining, by the DPN, a proximity of a UE based on a receivepower of the PRACH transmission associated with a detected set of rootsequences associated with one of the at least one base station in theneighbor list, and modifying operation of the DPN in response to theproximity.

Further aspects of the present disclosure are directed to an apparatusof wireless communication that includes means for establishingcommunication between a serving base station and a mobile device andmeans for transmitting, from the serving base station, a signal to themobile device served by the serving base station, wherein the signaltriggers periodic PRACH transmission from the mobile device.

Further aspects of the present disclosure are directed to an apparatusof wireless communication that includes means for receiving, at a mobiledevice, a signal from a serving base station and means for sendingperiodic PRACH transmissions from the mobile device in response to thesignal.

Further aspects of the present disclosure are directed to an apparatusof wireless communication that includes means for entering a reducedpower mode at a DPN, means for monitoring, by the DPN, for PRACHtransmissions from one or more UEs proximate to the DPN, means fordetecting a plurality of candidate PRACH transmissions, means forcombining the plurality of candidate PRACH transmissions at the DPN todetermine a detected PRACH transmission from a UE, means fordetermining, by the DPN, a proximity of the UE based on the detectedPRACH transmission, and means for modifying operation of the DPN inresponse to the proximity.

Further aspects of the present disclosure are directed to an apparatusof wireless communication that includes means for receiving, at aserving base station, a PRACH transmission from a mobile device andmeans for delaying, by the serving base station, transmission of a PRACHacknowledgement message to the mobile device.

Further aspects of the present disclosure are directed to an apparatusof wireless communication that includes means for entering a reducedpower mode at a DPN, means for monitoring, by the DPN, for a set of rootsequences associated with at least one base station in a neighbor listat the DPN, wherein the set of root sequences are located in PRACHtransmissions from one or more UEs, means for determining, by the DPN, aproximity of a UE based on a receive power of the PRACH transmissionassociated with a detected set of root sequences associated with one ofthe at least one base station in the neighbor list, and means formodifying operation of the DPN in response to the proximity.

Further aspects of the present disclosure are directed to a computerprogram product having a non-transitory computer-readable medium withprogram code stored thereon, wherein the program code, when executed bya computer, causes the computer to transmit, from a serving basestation, a signal to a mobile device served by the serving base station,wherein the signal triggers periodic PRACH transmission from the mobiledevice.

Further aspects of the present disclosure are directed to a computerprogram product having a non-transitory computer-readable medium withprogram code stored thereon, wherein the program code, when executed bya computer, causes the computer to receive, at a mobile device, a signalfrom a serving base station and send periodic PRACH transmissions fromthe mobile device in response to the signal.

Further aspects of the present disclosure are directed to a computerprogram product having a non-transitory computer-readable medium withprogram code stored thereon, wherein the program code, when executed bya computer, causes the computer to enter a reduced power mode at a DPN,monitor, by the DPN, for PRACH transmissions from one or more UEsproximate to the DPN, detect a plurality of candidate PRACHtransmissions, combine the plurality of candidate PRACH transmissions atthe DPN to determine a detected PRACH transmission from a UE, determine,by the DPN, a proximity of the UE based on the detected PRACHtransmission, and modify operation of the DPN in response to theproximity.

Further aspects of the present disclosure are directed to a computerprogram product having a non-transitory computer-readable medium withprogram code stored thereon, wherein the program code, when executed bya computer, causes the computer to receive, at a serving base station, aPRACH transmission from a mobile device and delay, by the serving basestation, transmission of a PRACH acknowledgement message to the mobiledevice.

Further aspects of the present disclosure are directed to a computerprogram product having a non-transitory computer-readable medium withprogram code stored thereon, wherein the program code, when executed bya computer, causes the computer to enter a reduced power mode at a DPN,monitor, by the DPN, for a set of root sequences associated with atleast one base station in a neighbor list at the DPN, wherein the set ofroot sequences are located in PRACH transmissions from one or more UEs,determine, by the DPN, a proximity of a UE based on a receive power ofthe PRACH transmission associated with a detected set of root sequencesassociated with one of the at least one base station in the neighborlist, and modify operation of the DPN in response to the proximity.

Further aspects of the present disclosure are directed to an apparatusincluding at least one processor and a memory coupled to the at leastone processor. The processor is configured to transmit, from a servingbase station, a signal to a mobile device served by the serving basestation, wherein the signal triggers periodic PRACH transmission fromthe mobile device.

Further aspects of the present disclosure are directed to an apparatusincluding at least one processor and a memory coupled to the at leastone processor. The processor is configured to receive, at a mobiledevice, a signal from a serving base station and send periodic PRACHtransmissions from the mobile device in response to the signal.

Further aspects of the present disclosure are directed to an apparatusincluding at least one processor and a memory coupled to the at leastone processor. The processor is configured to enter a reduced power modeat a DPN, monitor, by the DPN, for PRACH transmissions from one or moreUEs proximate to the DPN, detect a plurality of candidate PRACHtransmissions, combine the plurality of candidate PRACH transmissions atthe DPN to determine a detected PRACH transmission from a UE, determine,by the DPN, a proximity of the UE based on the detected PRACHtransmission, and modify operation of the DPN in response to theproximity.

Further aspects of the present disclosure are directed to an apparatusincluding at least one processor and a memory coupled to the at leastone processor. The processor is configured to receive, at a serving basestation, a PRACH transmission from a mobile device and delay, by theserving base station, transmission of a PRACH acknowledgement message tothe mobile device.

Further aspects of the present disclosure are directed to an apparatusincluding at least one processor and a memory coupled to the at leastone processor. The processor is configured to enter a reduced power modeat a DPN, monitor, by the DPN, for a set of root sequences associatedwith at least one base station in a neighbor list at the DPN, whereinthe set of root sequences are located in PRACH transmissions from one ormore UEs, determine, by the DPN, a proximity of a UE based on a receivepower of the PRACH transmission associated with a detected set of rootsequences associated with one of the at least one base station in theneighbor list, and modify operation of the DPN in response to theproximity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of amobile communication system.

FIG. 2 is a block diagram conceptually illustrating an example of adownlink frame structure in a mobile communication system.

FIG. 3 is a block diagram conceptually illustrating an exemplary framestructure in uplink LTE/-A communications.

FIG. 4 is a block diagram conceptually illustrating a design of a basestation/eNB and a UE configured according to one aspect of the presentdisclosure.

FIG. 5 is a call flow diagram illustrating a dynamic power node (DPN)activation procedure and utilizing UE transmission to activate a DPNaccording to an aspect of the present disclosure.

FIG. 6 is a call flow diagram illustrating a periodic PRACH triggerconfigured according to one aspect of the present disclosure.

FIG. 7 is a block diagram illustrating a wireless network configuredaccording to one aspect of the present disclosure.

FIG. 8 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure.

FIG. 9 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure.

FIG. 10 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure.

FIG. 11 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure.

FIG. 12 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure.

FIG. 13 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure.

FIG. 14 is a block diagram illustrating an eNB configured according toone aspect of the present disclosure.

FIG. 15 is a block diagram illustrating an UE configured according toone aspect of the present disclosure.

FIG. 16 is a block diagram illustrating an DNP configured according toone aspect of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to limit the scope of the disclosure.Rather, the detailed description includes specific details for thepurpose of providing a thorough understanding of the inventive subjectmatter. It will be apparent to those skilled in the art that thesespecific details are not required in every case and that, in someinstances, well-known structures and components are shown in blockdiagram form for clarity of presentation.

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology, suchas Universal Terrestrial Radio Access (UTRA), TelecommunicationsIndustry Association's (TIA's) CDMA2000®, and the like. The UTRAtechnology includes Wideband CDMA (WCDMA) and other variants of CDMA.The CDMA2000® technology includes the IS-2000, IS-95 and IS-856standards from the Electronics Industry Alliance (EIA) and TIA. A TDMAnetwork may implement a radio technology, such as Global System forMobile Communications (GSM). An OFDMA network may implement a radiotechnology, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB),IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, andthe like. The UTRA and E-UTRA technologies are part of Universal MobileTelecommunication System (UMTS). 3GPP Long Term Evolution (LTE) andLTE-Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA.UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents froman organization called the “3rd Generation Partnership Project” (3GPP).CDMA2000® and UMB are described in documents from an organization calledthe “3rd Generation Partnership Project 2” (3GPP2). The techniquesdescribed herein may be used for the wireless networks and radio accesstechnologies mentioned above, as well as other wireless networks andradio access technologies. For clarity, certain aspects of thetechniques are described below for LTE or LTE-A (together referred to inthe alternative as “LTE/-A”) and use such LTE/-A terminology in much ofthe description below.

FIG. 1 shows a wireless network 100 for communication, which may be anLTE-A network. The wireless network 100 includes a number of evolvednode Bs (eNBs) 110 and other network entities. An eNB may be a stationthat communicates with the UEs and may also be referred to as a basestation, a node B, an access point, and the like. Each eNB 110 mayprovide communication coverage for a particular geographic area. In3GPP, the term “cell” can refer to this particular geographic coveragearea of an eNB and/or an eNB subsystem serving the coverage area,depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell generally coversa relatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscriptions withthe network provider. A pico cell would generally cover a relativelysmaller geographic area and may allow unrestricted access by UEs withservice subscriptions with the network provider. A femto cell would alsogenerally cover a relatively small geographic area (e.g., a home) and,in addition to unrestricted access, may also provide restricted accessby UEs having an association with the femto cell (e.g., UEs in a closedsubscriber group (CSG), UEs for users in the home, and the like). An eNBfor a macro cell may be referred to as a macro eNB. An eNB for a picocell may be referred to as a pico eNB. And, an eNB for a femto cell maybe referred to as a femto eNB or a home eNB. In the example shown inFIG. 1, the eNBs 110 a, 110 b and 110 c are macro eNBs for the macrocells 102 a, 102 b and 102 c, respectively. The eNB 110 x is a pico eNBfor a pico cell 102 x. And, the eNBs 110 y and 110 z are femto eNBs forthe femto cells 102 y and 102 z, respectively. An eNB may support one ormultiple (e.g., two, three, four, and the like) cells.

The wireless network 100 also includes relay stations. A relay stationis a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., an eNB, a UE, or the like)and sends a transmission of the data and/or other information to adownstream station (e.g., another UE, another eNB, or the like). A relaystation may also be a UE that relays transmissions for other UEs. In theexample shown in FIG. 1, a relay station 110 r may communicate with theeNB 110 a and a UE 120 r, in which the relay station 110 r acts as arelay between the two network elements (the eNB 110 a and the UE 120 r)in order to facilitate communication between them. A relay station mayalso be referred to as a relay eNB, a relay, and the like.

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the eNBs may have similar frametiming, and transmissions from different eNBs may be approximatelyaligned in time. For asynchronous operation, the eNBs may have differentframe timing, and transmissions from different eNBs may not be alignedin time.

The UEs 120 are dispersed throughout the wireless network 100, and eachUE may be stationary or mobile. A UE may also be referred to as aterminal, a mobile station, a subscriber unit, a station, or the like. AUE may be a cellular phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, atablet computer, a laptop computer, a cordless phone, a wireless localloop (WLL) station, or the like. A UE may be able to communicate withmacro eNBs, pico eNBs, femto eNBs, relays, and the like. In FIG. 1, asolid line with double arrows indicates desired transmissions between aUE and a serving eNB, which is an eNB designated to serve the UE on thedownlink and/or uplink. A dashed line with double arrows indicatesinterfering transmissions between a UE and an eNB.

LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition the system bandwidth into multiple(K) orthogonal subcarriers, which are also commonly referred to astones, bins, or the like. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (K) may bedependent on the system bandwidth. For example, K may be equal to 72,180, 300, 600, 900, and 1200 for a corresponding system bandwidth of1.4, 3, 5, 10, 15, or 20 megahertz (MHz), respectively. The systembandwidth may also be partitioned into sub-bands. For example, asub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bandsfor a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 MHz,respectively.

FIG. 2 shows a downlink frame structure used in LTE/-A. The transmissiontimeline for the downlink may be partitioned into units of radio frames.Each radio frame may have a predetermined duration (e.g., 10milliseconds (ms)) and may be partitioned into 10 subframes with indicesof 0 through 9. Each subframe may include two slots. Each radio framemay thus include 20 slots with indices of 0 through 19. Each slot mayinclude L symbol periods, e.g., 7 symbol periods for a normal cyclicprefix (as shown in FIG. 2) or 6 symbol periods for an extended cyclicprefix. The 2L symbol periods in each subframe may be assigned indicesof 0 through 2L−1. The available time frequency resources may bepartitioned into resource blocks. Each resource block may cover Nsubcarriers (e.g., 12 subcarriers) in one slot.

In LTE/-A, an eNB may send a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) for each cell in the eNB. Theprimary and secondary synchronization signals may be sent in symbolperiods 6 and 5, respectively, in each of subframes 0 and 5 of eachradio frame with the normal cyclic prefix, as shown in FIG. 2. Thesynchronization signals may be used by UEs for cell detection andacquisition. The eNB may send a Physical Broadcast Channel (PBCH) insymbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carrycertain system information.

The eNB may send a Physical Control Format Indicator Channel (PCFICH) inthe first symbol period of each subframe, as seen in FIG. 2. The PCFICHmay convey the number of symbol periods (M) used for control channels,where M may be equal to 1, 2 or 3 and may change from subframe tosubframe. M may also be equal to 4 for a small system bandwidth, e.g.,with less than 10 resource blocks. In the example shown in FIG. 2, M=3.The eNB may send a Physical HARQ Indicator Channel (PHICH) and aPhysical Downlink Control Channel (PDCCH) in the first M symbol periodsof each subframe. The PDCCH and PHICH are also included in the firstthree symbol periods in the example shown in FIG. 2. The PHICH may carryinformation to support hybrid automatic retransmission (HARQ). The PDCCHmay carry information on resource allocation for UEs and controlinformation for downlink channels. The eNB may send a Physical DownlinkShared Channel (PDSCH) in the remaining symbol periods of each subframe.The PDSCH may carry data for UEs scheduled for data transmission on thedownlink.

In addition to sending PHICH and PDCCH in the control section of eachsubframe, i.e., the first symbol period of each subframe, the LTE-A mayalso transmit these control-oriented channels in the data portions ofeach subframe as well. As shown in FIG. 2, these new control designsutilizing the data region, e.g., the Relay-Physical Downlink ControlChannel (R-PDCCH) and Relay-Physical HARQ Indicator Channel (R-PHICH)are included in the later symbol periods of each subframe. The R-PDCCHis a new type of control channel utilizing the data region originallydeveloped in the context of half-duplex relay operation. Different fromlegacy PDCCH and PHICH, which occupy the first several control symbolsin one subframe, R-PDCCH and R-PHICH are mapped to resource elements(REs) originally designated as the data region. The new control channelmay be in the form of Frequency Division Multiplexing (FDM), TimeDivision Multiplexing (TDM), or a combination of FDM and TDM.

The eNB may send the PSS, SSS and PBCH in the center 1.08 MHz of thesystem bandwidth used by the eNB. The eNB may send the PCFICH and PHICHacross the entire system bandwidth in each symbol period in which thesechannels are sent. The eNB may send the PDCCH to groups of UEs incertain portions of the system bandwidth. The eNB may send the PDSCH tospecific UEs in specific portions of the system bandwidth. The eNB maysend the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner to allUEs, may send the PDCCH in a unicast manner to specific UEs, and mayalso send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period.Each resource element may cover one subcarrier in one symbol period andmay be used to send one modulation symbol, which may be a real orcomplex value. Resource elements not used for a reference signal in eachsymbol period may be arranged into resource element groups (REGs). EachREG may include four resource elements in one symbol period. The PCFICHmay occupy four REGs, which may be spaced approximately equally acrossfrequency, in symbol period 0. The PHICH may occupy three REGs, whichmay be spread across frequency, in one or more configurable symbolperiods. For example, the three REGs for the PHICH may all belong insymbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCHmay occupy 9, 18, 32 or 64 REGs, which may be selected from theavailable REGs, in the first M symbol periods. Only certain combinationsof REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. TheUE may search different combinations of REGs for the PDCCH. The numberof combinations to search is typically less than the number of allowedcombinations for the PDCCH. An eNB may send the PDCCH to the UE in anyof the combinations that the UE will search.

A UE may be within the coverage of multiple eNBs. One of these eNBs maybe selected to serve the UE. The serving eNB may be selected based onvarious criteria such as received power, path loss, signal-to-noiseratio (SNR), etc.

FIG. 3 is a block diagram illustrating an exemplary frame structure 300in uplink long term evolution (LTE/-A) communications. The availableresource blocks (RBs) for the uplink may be partitioned into a datasection and a control section. The control section may be formed at thetwo edges of the system bandwidth and may have a configurable size. Theresource blocks in the control section may be assigned to UEs fortransmission of control information. The data section may include allresource blocks not included in the control section. The design in FIG.3 results in the data section including contiguous subcarriers, whichmay allow a single UE to be assigned all of the contiguous subcarriersin the data section.

A UE may be assigned resource blocks in the control section to transmitcontrol information to an eNB. The UE may also be assigned resourceblocks in the data section to transmit data to the eNode B. The UE maytransmit control information in a Physical Uplink Control Channel(PUCCH) on the assigned resource blocks 310 a and 310 b in the controlsection. The UE may transmit only data or both data and controlinformation in a Physical Uplink Shared Channel (PUSCH) on the assignedresource blocks 320 a and 320 b in the data section. An uplinktransmission may span both slots of a subframe and may hop acrossfrequency as shown in FIG. 3.

Referring back to FIG. 1, the wireless network 100 uses the diverse setof eNBs 110 (i.e., macro eNBs, pico eNBs, femto eNBs, and relays) toimprove the spectral efficiency of the system per unit area. Because thewireless network 100 uses such different eNBs for its spectral coverage,it may also be referred to as a heterogeneous network. The macro eNBs110 a-c are usually carefully planned and placed by the provider of thewireless network 100. The macro eNBs 110 a-c generally transmit at highpower levels (e.g., 5 W-40 W). The pico eNB 110 x and the relay station110 r, which generally transmit at substantially lower power levels(e.g., 100 mW-2 W), may be deployed in a relatively unplanned manner toeliminate coverage holes in the coverage area provided by the macro eNBs110 a-c and improve capacity in the hot spots. The femto eNBs 110 y-z,which are typically deployed independently from the wireless network 100may, nonetheless, be incorporated into the coverage area of the wirelessnetwork 100 either as a potential access point to the wireless network100, if authorized by their administrator(s), or at least as an activeand aware eNB that may communicate with the other eNBs 110 of thewireless network 100 to perform resource coordination and coordinationof interference management. The femto eNBs 110 y-z typically alsotransmit at substantially lower power levels (e.g., 100 mW-2 W) than themacro eNBs 110 a-c.

In operation of a heterogeneous network, such as the wireless network100, each UE is usually served by the eNB 110 with the better signalquality, while the unwanted signals received from the other eNBs 110 aretreated as interference. While such operational principals can lead tosignificantly sub-optimal performance, gains in network performance arerealized in the wireless network 100 by using intelligent resourcecoordination among the eNBs 110, better server selection strategies, andmore advanced techniques for efficient interference management.

A pico eNB, such as the pico eNB 110 x, is characterized by asubstantially lower transmit power when compared with a macro eNB, suchas the macro eNBs 110 a-c. A pico eNB will also usually be placed arounda network, such as the wireless network 100, in an ad hoc manner.Because of this unplanned deployment, wireless networks with pico eNBplacements, such as the wireless network 100, can be expected to havelarge areas with low signal to interference conditions, which can makefor a more challenging RF environment for control channel transmissionsto UEs on the edge of a coverage area or cell (a “cell-edge” UE).Moreover, the potentially large disparity (e.g., approximately 20 dB)between the transmit power levels of the macro eNBs 110 a-c and the picoeNB 110 x implies that, in a mixed deployment, the downlink coveragearea of the pico eNB 110 x will be much smaller than that of the macroeNBs 110 a-c.

In the uplink case, however, the signal strength of the uplink signal isgoverned by the UE, and, thus, will be similar when received by any typeof the eNBs 110. With the uplink coverage areas for the eNBs 110 beingroughly the same or similar, uplink handoff boundaries will bedetermined based on channel gains. This can lead to a mismatch betweendownlink handover boundaries and uplink handover boundaries. Withoutadditional network accommodations, the mismatch would make the serverselection or the association of UE to eNB more difficult in the wirelessnetwork 100 than in a macro eNB-only homogeneous network, where thedownlink and uplink handover boundaries are more closely matched.

If server selection is based predominantly on downlink received signalstrength, the usefulness of mixed eNB deployment of heterogeneousnetworks, such as the wireless network 100, will be greatly diminished.This is because the larger coverage area of the higher powered macroeNBs, such as the macro eNBs 110 a-c, limits the benefits of splittingthe cell coverage with the pico eNBs, such as the pico eNB 110 x,because, the higher downlink received signal strength of the macro eNBs110 a-c will attract all of the available UEs, while the pico eNB 110 xmay not be serving any UE because of its much weaker downlinktransmission power. Moreover, the macro eNBs 110 a-c will likely nothave sufficient resources to efficiently serve those UEs. Therefore, thewireless network 100 will attempt to actively balance the load betweenthe macro eNBs 110 a-c and the pico eNB 110 x by expanding the coveragearea of the pico eNB 110 x. This concept is referred to as cell rangeextension (CRE).

The wireless network 100 achieves CRE by changing the manner in whichserver selection is determined. Instead of basing server selection ondownlink received signal strength, selection is based more on thequality of the downlink signal. In one such quality-based determination,server selection may be based on determining the eNB that offers theminimum path loss to the UE. Additionally, the wireless network 100provides a fixed partitioning of resources between the macro eNBs 110a-c and the pico eNB 110 x. However, even with this active balancing ofload, downlink interference from the macro eNBs 110 a-c should bemitigated for the UEs served by the pico eNBs, such as the pico eNB 110x. This can be accomplished by various methods, including interferencecancellation at the UE, resource coordination among the eNBs 110, or thelike.

In a heterogeneous network with cell range extension, such as thewireless network 100, in order for UEs to obtain service from thelower-powered eNBs, such as the pico eNB 110 x, in the presence of thestronger downlink signals transmitted from the higher-powered eNBs, suchas the macro eNBs 110 a-c, the pico eNB 110 x engages in control channeland data channel interference coordination with the dominant interferingones of the macro eNBs 110 a-c. Many different techniques forinterference coordination may be employed to manage interference. Forexample, inter-cell interference coordination (ICIC) may be used toreduce interference from cells in co-channel deployment. One ICICmechanism is adaptive resource partitioning. Adaptive resourcepartitioning assigns subframes to certain eNBs. In subframes assigned toa first eNB, neighbor eNBs do not transmit. Thus, interferenceexperienced by a UE served by the first eNB is reduced. Subframeassignment may be performed on both the uplink and downlink channels.

For example, subframes may be allocated between three classes ofsubframes: protected subframes (U subframes), prohibited subframes (Nsubframes), and common subframes (C subframes). Protected subframes maybe assigned to a first eNB for use exclusively by the first eNB.Protected subframes may also be referred to as “clean” subframes basedon the lack of interference from neighboring eNBs. Prohibited subframesmay be subframes assigned to a neighbor eNB, and the first eNB isprohibited from transmitting data during the prohibited subframes. Forexample, a prohibited subframe of the first eNB may correspond to aprotected subframe of a second interfering eNB. Thus, the first eNB isthe only eNB transmitting data during the first eNB's protectedsubframe. Common subframes may be used for data transmission by multipleeNBs. Common subframes may also be referred to as “unclean” subframesbecause of the possibility of interference from other eNBs.

Heterogeneous networks may have eNBs of different power classes. Forexample, three power classes may be defined, in decreasing power class,as macro eNBs, pico eNBs, and femto eNBs. When macro eNBs, pico eNBs,and femto eNBs are in a co-channel deployment, the power spectraldensity (PSD) of the macro eNB (aggressor eNB) may be larger than thePSD of the pico eNB and the femto eNB (victim eNBs) creating largeamounts of interference with the pico eNB and the femto eNB. Protectedsubframes may be used to reduce or minimize interference with the picoeNBs and femto eNBs. That is, a protected subframe may be scheduled forthe victim eNB to correspond with a prohibited subframe on the aggressoreNB.

In deployments of heterogeneous networks, such as the wireless network100, a UE may operate in a dominant interference scenario in which theUE may observe high interference from one or more interfering eNBs. Adominant interference scenario may occur due to restricted association.For example, in FIG. 1, the UE 120 y may be close to the femto eNB 110 yand may have high received power for the eNB 110 y. However, the UE 120y may not be able to access the femto eNB 110 y due to restrictedassociation and may then connect to the macro eNB 110 c (as shown inFIG. 1) or to the femto eNB 110 z also with lower received power (notshown in FIG. 1). The UE 120 y may then observe high interference fromthe femto eNB 110 y on the downlink and may also cause high interferenceto the eNB 110 y on the uplink. Using coordinated interferencemanagement, the eNB 110 c and the femto eNB 110 y may communicate overthe backhaul 134 to negotiate resources. In the negotiation, the femtoeNB 110 y agrees to cease transmission on one of its channel resources,such that the UE 120 y will not experience as much interference from thefemto eNB 110 y as it communicates with the eNB 110 c over that samechannel.

In addition to the discrepancies in signal power observed at the UEs insuch a dominant interference scenario, timing delays of downlink signalsmay also be observed by the UEs, even in synchronous systems, because ofthe differing distances between the UEs and the multiple eNBs. The eNBsin a synchronous system are presumptively synchronized across thesystem. However, for example, considering a UE that is a distance of 5km from the macro eNB, the propagation delay of any downlink signalsreceived from that macro eNB would be delayed approximately 16.67 μs (5km÷3×10⁸, i.e., the speed of light, ‘c’). Comparing that downlink signalfrom the macro eNB to the downlink signal from a much closer femto eNB,the timing difference could approach the level of a time-to-live (TTL)error.

Additionally, such timing difference may impact the interferencecancellation at the UE. Interference cancellation often uses crosscorrelation properties between a combination of multiple versions of thesame signal. By combining multiple copies of the same signal,interference may be more easily identified because, while there willlikely be interference on each copy of the signal, it will likely not bein the same location. Using the cross correlation of the combinedsignals, the actual signal portion may be determined and distinguishedfrom the interference, thus, allowing the interference to be canceled.

FIG. 4 shows a block diagram of a design of a base station/eNB 110 and aUE 120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. For a restricted association scenario, the eNB 110 may be themacro eNB 110 c in FIG. 1, and the UE 120 may be the UE 120 y. The eNB110 may also be a base station of some other type. The eNB 110 may beequipped with antennas 434 a through 434 t, and the UE 120 may beequipped with antennas 452 a through 452 r.

At the eNB 110, a transmit processor 420 may receive data from a datasource 412 and control information from a controller/processor 440. Thecontrol information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. Thedata may be for the PDSCH, etc. The transmit processor 420 may process(e.g., encode and symbol map) the data and control information to obtaindata symbols and control symbols, respectively. The transmit processor420 may also generate reference symbols, e.g., for the PSS, SSS, andcell-specific reference signal. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 430 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols, if applicable, and may provide output symbol streamsto the modulators (MODS) 432 a through 432 t. Each modulator 432 mayprocess a respective output symbol stream (e.g., for OFDM, etc.) toobtain an output sample stream. Each modulator 432 may further process(e.g., convert to analog, amplify, filter, and upconvert) the outputsample stream to obtain a downlink signal. Downlink signals frommodulators 432 a through 432 t may be transmitted via the antennas 434 athrough 434 t, respectively.

At the UE 120, the antennas 452 a through 452 r may receive the downlinksignals from the eNB 110 and may provide received signals to thedemodulators (DEMODs) 454 a through 454 r, respectively. Eachdemodulator 454 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 454 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 456 may obtainreceived symbols from all the demodulators 454 a through 454 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 458 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 460, and provide decoded control informationto a controller/processor 480.

On the uplink, at the UE 120, a transmit processor 464 may receive andprocess data (e.g., for the PUSCH) from a data source 462 and controlinformation (e.g., for the PUCCH) from the controller/processor 480. Thetransmit processor 464 may also generate reference symbols for areference signal. The symbols from the transmit processor 464 may beprecoded by a TX MIMO processor 466 if applicable, further processed bythe demodulators 454 a through 454 r (e.g., for SC-FDM, etc.), andtransmitted to the eNB 110. At the eNB 110, the uplink signals from theUE 120 may be received by the antennas 434, processed by the modulators432, detected by a MIMO detector 436 if applicable, and furtherprocessed by a receive processor 438 to obtain decoded data and controlinformation sent by the UE 120. The processor 438 may provide thedecoded data to a data sink 439 and the decoded control information tothe controller/processor 440.

The controllers/processors 440 and 480 may direct the operation at theeNB 110 and the UE 120, respectively. The controller/processor 440and/or other processors and modules at the eNB 110 may perform or directthe execution of various processes for the techniques described herein.The controllers/processor 480 and/or other processors and modules at theUE 120 may also perform or direct the execution of the functional blocksillustrated in FIGS. 8-13, and/or other processes for the techniquesdescribed herein. The memories 442 and 482 may store data and programcodes for the eNB 110 and the UE 120, respectively. A scheduler 444 mayschedule UEs for data transmission on the downlink and/or uplink.

In heterogeneous networks and networks in which multiple access nodes,base stations, and eNBs may be available for providing communications toone or more UEs, it may be beneficial for such nodes to reduce powerwhen no UEs are being served or when the number of UEs being servedfalls well below the loading capacity. Various nodes may includeenergy-saving features that allows a low-power mode of operation, suchas turning off completely, reducing transmission signal duty cycle,reducing transmission power, and the like, or facilitates uplink (UL)enhanced ICIC (eICIC), and the like.

With various nodes implementing such power-saving low-powered modes, itis desirable to define a node activation procedure based on proximitydetection of active UEs. The present disclosure provides enhancedsolutions that utilize transmissions on existing physical uplink (UL)channels for detection of active UEs. The physical uplink channeltransmissions may include a random access channel transmission, such asa physical random access channel (PRACH) signature sequence, or areference signal, such as a sounding reference signal (SRS).

FIG. 5 is a call flow diagram illustrating a dynamic power node (DPN)activation procedure and utilizing UE transmission to activate a DPNaccording to an aspect of the present disclosure. As illustrated in FIG.5, the donor eNB 510 may include a radio resource management (RRM)server 505. The donor eNB 510 may configure the DPN 520 with activationparameters at time 540. The activation parameters may indicatemonitoring conditions (e.g., physical uplink transmissions from UE 530such as a PRACH signature sequence, SRS, or the like) to detect UEproximity.

A DPN is any various type of base station or access point that mayreduce power during periods of inactivity or low activity and, upondetection of a nearby UE, may increase power to participate incommunication with the detected UE. A DPN may be a small cell, such as apico eNB, femto eNB, relay, user eNb (UeNB) (a UE that may be configuredas a base station or eNB to other proximate mobile devices), and thelike, or may be a large cell, such as a macro eNB, and the like. Theexample implementations illustrated in the various figures herein mayrefer to an access point, UeNB, or the like. However, these are merelyintended to represent example implementations and those skilled in theart will readily recognize that any type of base station or access pointmay be used within the scope of the various aspects.

The donor eNB 510 may optionally trigger the UE 530 to transmit on thephysical uplink channel. For example, the donor eNB 510 may transmit acontrol channel order, such as a PDCCH order at time 550, to trigger thetransmission of a PRACH signature sequence (or SRS) from the UE 530.Rather than dynamically triggering the uplink transmission, the uplinktransmission may be semi-statically configured.

In response to receiving the uplink trigger (e.g., control channelorder), the UE 530 transmits (e.g., a PRACH signature sequence, SRS, orthe like) on a physical channel at time 560. The DPN 520 may detect theuplink transmission from the UE 530 at time 570. If the uplinktransmission satisfies thresholds (e.g., threshold values provided inthe activation parameters) the DPN 520 can begin either networkactivation or autonomous activation.

For network activation, the DPN 520 transmits an activation request attime 580 to the donor eNB 510. In response to receiving the activationrequest, the donor eNB 510 may transmit an activation grant at time 590to the DPN 520 so that the relay may power up at time 595. Withautonomous activation, the flow proceeds from time 570 directly to time595 where the DPN 520 automatically activates.

As discussed above, according to one aspect the donor eNB 510 mayconfigure the DPN 520 with activation parameters. The activationparameters enable the DPN 520 to detect the UE 530 proximity. Theseparameters may include a PRACH signature sequence space, time/frequencyresources, or other uplink sounding transmission signal parameters suchas those related to an SRS. For PRACH parameters, the DPN 520 may beconfigured based on the serving cell PRACH configuration and optionallythe PRACH configuration of a neighboring cell(s). The activationparameters can also include threshold values, such a minimum signalstrength above which the UE 530 is considered to be proximate enough towarrant activating the relay. Alternatively or in addition, interferencethreshold values can be provided.

As illustrated in FIG. 5, the donor eNB 510 may dynamically trigger theUE 530 to transmit on the uplink, e.g., with a PRACH transmission, SRS,or the like, using a reserved set of signature sequences and time and/orfrequency resources. The triggering can be based on criteria observed bythe donor eNB 510, such as data load, radio conditions, etc. That is,the donor eNB 510 may only transmit the uplink trigger for UEs with ahigh downlink data load and when the network is loaded. Alternatively,the donor eNB 510 may semi-statically configure periodic or event basedtrigger of uplink transmissions during network setup.

It should be noted that the DPN 520 may search for the uplinktransmissions, such as a PRACH signal, SRS, or the like, based on allpossible configurations. Nonetheless, the number of possibleconfigurations is a limited number.

According to one aspect, the relay may further be limited to search fordedicated preambles activated with an uplink trigger, such as the PDCCHorder. Because the DPN 520 is searching for a reserved set of signaturesequences, the DPN 520 will not be activated due to uplink transmissions(e.g., PRACH transmissions, SRS, or the like) sent during an initialaccess phase of a UE 530.

One advantage of PRACH signature sequences is that they handle timinguncertainty by design because the cyclic prefix of a PRACH signaturesequence is large.

As further illustrated in FIG. 5, according to one aspect, the UE 530may transmit an uplink message, such as a PRACH signature sequence, SRS,or the like. The uplink transmission may be on the same carrierfrequency used for uplink data transmission to the donor eNB 510 (e.g.,2 GHz) or a carrier frequency of an access link to the DPN 520 (e.g.,3.6 GHz). The UE 530 may be configured to select a PRACH signaturesequence from a pool of signature sequences to convey additionalinformation from the UE 530, such as radio conditions, data loading, orpower headroom (e.g., transmission power). According to some aspects,the uplink transmission is transmitted with full power or a fixed powerlevel.

A DPN detects the uplink transmissions, such as the PRACH transmissions,SRS, or the like, transmitted by the UEs intended for other nodes. Tothe UE, the uplink signal request transmitted by the serving eNB simplytriggers the random access procedure causing transmission of the PRACHor signals transmission of SRS, and the like. In various aspects of thepresent disclosure, the UE may not know that the requested PRACH, SRS,or other such requested uplink signal transmissions are intended for DPNactivation. The UE receives the PDCCH order from the serving eNB thattriggers the uplink signals, and the UE transmits the signals. The DPNmay know the resources where preambles intended for the other nodes aresent and may also potentially know the preamble identifiers (IDs) aswell, either dynamically, such as through backhaul coordination, orsemi-statically, such as through network standards or via originalequipment manufacturing (OEM) information settings. These resourcesand/or the preamble IDs may be used by a DPN to determine an identity ofthe UE transmitting the preamble, or of the corresponding serving eNB.The identity may include a network-wide identity or property, such asthe standards capabilities of the UE (e.g., Rel-8, Rel-10, and thelike).

Aspects of the present disclosure provide for periodic uplink signaltransmission without necessity for individual signal orders. Instead ofrequiring a single PDCCH order for each PRACH or SRS transmission,signaling from the serving eNB triggers periodic uplink signaltransmissions. For purposes of this disclosure periodic PRACH refers toperiodic initiation of new PRACH procedures in which each is independentof the previous transmissions. The single triggering signal from theserving base station triggers multiple periodic uplink signaltransmissions from the UE in which the periodicity may be set by thetriggering.

FIG. 6 is a call flow diagram illustrating a periodic PRACH triggerconfigured according to one aspect of the present disclosure. UE 600 isserved by eNB 602. A DPN 601 in a reduced power mode monitors for PRACHtransmissions from nearby UEs that it may serve or provide carriersupport. At time 603, eNB 602 transmits a PRACH trigger signal to UE600. The PRACH trigger signal may be various signal types of layer 2 or3, such as a radio resource control (RRC) of layer 3, or a PDCCH oflayer 2. The trigger signal triggers a periodic PRACH transmission fromUE 600. UE 600 begins transmitting PRACH at time 605. As illustrated, UE600 also transmits at times 606-608. The PRACH signals transmitted by UE600 at times 606-608 do not rely on individual PDCCH signals. As thePRACH signals are transmitted from UE 600, DPN 601 monitors and detectsthe signals at times 605-608. DPN 601 may activate after detecting anyof the PRACH signals at times 605-608. Alternatively, DPN 601 maycombine the PRACH signals at time 605-608 to increase reliability of thedetection.

The trigger signal from eNB 602 may provide an on/off trigger. Forexample, the trigger signal at time 603 triggers UE 600 to begintransmitting the PRACH signals at times 605-608. At alternate time 609,eNB 602 transmits another trigger signal which indicates to UE 600 tostop transmitting PRACH signals.

In alternative aspects, the trigger signal from eNB 602 at time 603includes signal settings that UE 600 uses in generating and managingPRACH signals. On receipt of the trigger signal at time 603, UE 600 alsoimplements the PRACH setting 604 for its PRACH transmissions. Thesesettings may provide a duration and interval for the semi-persistentPRACH transmissions. For example, the trigger signal at time 603includes instructions and settings for the UE 600, includingestablishing the periodicity of the PRACH signal, signature sequenceset, transmit power change with regard to any open loop power sequences,and the like. The settings may also provide reference signal receivepower (RSRP) thresholds that indicate when the UE 600 is to transmit thePRACH signals.

The proximity of the UE to the DPN is determined by estimating the roughdistance, such as through the path loss, from the UE to the DPN. Inorder to estimate the distance, both the received power and estimatedtransmission power of the PRACH are used by the DPN. However, thetransmission power for PRACH is not fixed. Currently, the PRACHtransmission power is based on the downlink path loss estimatedetermined by the UE. Accordingly, the estimated distance may beunreliable, which causes the proximity detection by the DPN to be lessreliable that desirable.

In additional aspects of the present disclosure, the trigger signal sentat time 603 may include an indication for UE 600 to transmit the PRACHat a fixed power. The fixed power may be a specific power setting orsimply and indication to transmit at the maximum power. Thus, when UE600 receives the trigger signal with the proximity detection powerindication, UE 600 sets the transmission power according to the fixedrules (e.g., maximum power, pre-determined fixed power), and transmitsthe PRACH using the fixed power instead of the current path-loss-basedpower rules. The use of fixed power in the UE PRACH procedure providesthe DNP 601 with a reliable mechanism by which to gauge the proximity tothe transmitting UE 600.

It should be noted that in alternative aspects of the presentdisclosure, the example illustrated in FIG. 6 may be implemented usingSRS or other types of uplink signals for facilitating proximitydetection by the DPN instead of PRACH transmissions.

It should further be noted that the trigger signaling from eNB 602 attime 603 may also include identification to the UE 600 that thetriggered PRACH or other uplink signals, such as SRS, and the like, arefor proximity detection and prompts the UE 600 to continue decoding anyPDCCH data that it receives. In a typical PRACH procedure, a UE willdiscontinue decoding PDCCH until the communication session isreestablished. Having the trigger signal inform UE 600 to continuedecoding, there may be not additional communication delays caused by thesuspension of decoding. For example, as UE 600 implements the PRACHsettings 604, one of the settings informs UE 600 to continue decoding.At alternative time 610, eNB 602 transmits a PDCCH with downlink data.UE 600, while still in the process of transmitting periodic PRACH,decodes the PDCCH at 611. UE 600 will also decode the PDCCH at 613 sentfrom eNB 602 at time 612. Thus, in the described aspect of thedisclosure, UE 600 will continue to decode PDCCH even though it isplaced into a periodic PRACH transmission procedure.

It should be noted that the signal to continue decoding PDCCH mayinclude a distinct signal transmitted in the trigger signal from eNB602. It may also be a procedure interpreted by the UE 600 simply basedon receiving the trigger signal from eNB 602.

FIG. 7 is a block diagram illustrating a wireless network 70 configuredaccording to one aspect of the present disclosure. Wireless network 70includes UE 701 served by serving eNB 700. Serving eNB 700 transmits aPRACH trigger signal 704 to UE 701, which may be an RRC signal or aPDCCH that includes an order for PRACH from UE 701. In response, UE 701begins periodically transmitting PRACH signals 705. DPN 702 and UeNB 703are currently in a powered-down mode, but are monitoring for PRACHsignals for proximate UEs. DPN 702 and UeNB 703 may detect PRACH signals705 according to PRACH-based proximity procedures. It should be notedthat DPN 702 and UeNB 703 may be the same entity (e.g., a DPN may be anUeNB).

According to aspects of the present disclosure, instead of transmittingthe PRACH acknowledgment message (e.g., msg2) immediately upon receivingthe first transmission of PRACH signals 705, serving eNB 700 delaystransmission of the acknowledgment message. Without receiving the PRACHacknowledgement message, UE 701 repeats transmission of PRACH signals705. With multiple PRACH transmissions, DPN 702 and UeNB 703 are able todetect multiple PRACH signals, which improves the probability ofaccurate detection and analysis of the PRACH transmission. Moreover, invarious aspects, UE 701 may increase transmit power with each successivetransmission of PRACH signals 705, as it may believe the signal was notsuccessfully received by serving eNB 700. Thus, DPN 702 and UeNB 703will additionally increase the probability of success detection andprocessing of the PRACH transmission.

Serving eNB 700 may control the delay in transmission of the PRACHacknowledgement in various ways. For example, serving eNB 700 may begina timer when the first of PRACH signals 705 is received. Afterexpiration of the timer, serving eNB 700 will transmit the PRACHacknowledgement, which causes UE 701 to stop transmitting PRACH signals705.

According to additional aspects of the present disclosure, DPN 702 andUeNB 703 are configured to monitor root sequences from multiple neighborbase stations, rather than sequentially assigned root sequences, asspecified in the current LTE standards. The set of monitored rootsequences may be semi-statically set network-wide or may be speciallymaintained for PRACH-based proximity. Moreover, the sets of rootsequences change when DPN 702 and UeNB 703 are in a fully-powered eNBstate. In order to better manage the sets of root sequences, a neighborlist is maintained at DPN 702 and UeNB 703. The neighbor list mayinclude the set of neighbor base stations for which root sequences aremonitored for the sake of PRACH-based proximity detection. For example,the neighbor list maintained by DPN 702 and UeNB 703 may includeneighboring base stations, such as eNBs 706-707 and access node 708.

In certain aspects of the present disclosure, such a neighbor list maybe configured by the network operator or administrator, or theparticular DPN, such as DPN 702 and UeNB 703, may autonomously determinethe nearby base stations and build the neighbor list using downlinkmeasurements, such as the downlink measurements made by UeNB 703, orthrough network listening, such as the network listening performed byDPN 702. Additionally, a neighbor list may be dynamically adapted basedon certain network events, such as a UE being handed over to/from amacro base station, such as serving base station 700 or eNBs 706-707from/to a DPN, such as DPN 702 and UeNB 703.

In various aspects of the present disclosure, neighbor-specificthresholds may be associated with each neighbor base station in aneighbor list maintained for PRACH-based proximity detection. The DPN,such as DPN 702 and UeNB 703, compares the received PRACH power with theassigned threshold correspond to the particular base station to whichthe UE is sending the PRACH signal. When the threshold is met for anyparticular base station in the neighbor list, the DPN will determineproximity and switch into the fully-powered active mode.

Different thresholds are assigned to different base stations in theneighbor list because of the different propagation conditions, antennaconfigurations, and the like, that may be present. Moreover, due togeographic features, such as mountains, buildings, and the like, thefootprint of any particular base station may be irregular, non-uniform,or asymmetrically laid out. The thresholds are determined based on theseconsideration. For example, with respect to the neighbor list maintainedby UeNB 703, the threshold associated with serving eNB 700 may be lowerthan the threshold associated with eNB 706 because eNB 706 is closer toUeNB 703. Thus, if eNB 706 is serving UE 701 and sends PRACH order 709,the PRACH signals 710 detected by UeNB 703 will need to have a lowerreceived power to trigger full activation of UeNB 703 than the receivepower of PRACH signals 705, when PRACH signals are sent to and UE 701 isserved by serving eNB 700.

It should be noted that in alternative aspects of the presentdisclosure, the example illustrated in FIG. 7 may be implemented usingSRS or other types of uplink signals for facilitating proximitydetection by a DPN instead of PRACH transmissions.

FIG. 8 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure. At block800, communication is established between a base station and a mobiledevice. With reference to FIG. 14, a block diagram of an eNB 602 isillustrated configured according to one aspect of the presentdisclosure. In example of the blocks presented in FIG. 8, eNB 602includes a controller/processor 440 which executes logic stored inmemory 442 and controls components that define the features andfunctionality of eNB 602. ENB 602 further includes wireless radios 1400and signal generator 1401. Wireless radios 1400 may include individualcomponents as illustrated further in FIG. 4. Signal generator 1401 mayinclude individual components, such as transmit processor 420. Undercontrol of controller/processor 440, eNB 602 generates signals usingsignal generator 1401 and transmits those signals to a UE being servedby eNB 602 using wireless radios 1400.

At block 801, the serving base station transmits a signal to a mobiledevice, wherein the signal triggers periodic PRACH transmission from themobile device. For example, controller/processor 440 executesPRACH-based proximity logic 1402, stored in memory 442, which operatesfunctionality to generate a trigger signal that triggers the served UEto begin periodic PRACH transmissions. In selected aspects, theoperating functionality of PRACH-based proximity logic 1402 may accessPRACH settings 1403 which includes settings information for the PRACHsignals within the trigger signal for the UE to use in generating andtransmitting the periodic PRACH signals, such as periodicity, duration,transmit power, RSRP threshold information, and the like. Under controlof controller/processor 440, eNB 602 generates the trigger signal atsignal generator 1401, which may generate the trigger signal as avariety of signals, including a layer 3 signal (e.g., RRC), a layer 2signal (e.g., PDCCH). The trigger signal is then transmitted to the UEvia wireless radios 1400.

At optional block 802, a DPN determines proximity of the mobile devicebased on detection of the periodic PRACH transmissions triggered by theserving base station. Optional block 802 provides functionality for aDPN similar to the functionality illustrated at block 1004 of FIG. 10.For example, eNB 110 may represent the components of a DPN, such as DPN601. In such a representation, controller/processor 440 of DPN 601, inexecution of PRACH-based proximity logic 1603 (FIG. 16), stored inmemory 442, creates an operating environment that monitors for signalsreceived through antennas 434 a-t that are demodulated, bydemodulator/modulators 432 a-t, and determined to be the periodic PRACHsignals transmitted by the mobile device. Detection of the periodicPRACH signals prompts the operating environment of the PRACH-basedproximity logic 1603, under control of controller/processor 440, todetermine that the mobile device is proximate to the serving basestation.

FIG. 9 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure. At block900, a mobile device receives a signal from a serving base station. Withreference to FIG. 15, a block diagram of a UE 600 is illustratedconfigured according to one aspect of the present disclosure. In exampleof the blocks presented in FIG. 9, UE 600 includes acontroller/processor 480 which executes logic stored in memory 482 andcontrols components that define the features and functionality of UE600. UE 600 further includes wireless radios 1500 and signal generator1501. Wireless radios 1500 may include individual components asillustrated further in FIG. 4. Signal generator 1501 may includeindividual components, such as transmit processor 464. Radio frequencysignals received and demodulated through wireless radios 1500 may bedecoded under control of controller/processor 480 as a trigger signalfor triggering PRACH transmissions.

At block 901, the mobile device sends periodic PRACH transmissions inresponse to the signal. For example, in response to the trigger signal,controller/processor 480 executes PRACH signaling logic 1502, as storedin memory 482. The executing environment of PRACH signaling logic 1502causes UE 600 to generate a periodic PRACH signal using signal generator1501. In generating the periodic PRACH signal, the executing environmentof PRACH signaling logic 1502 accesses PRACH settings 1503, in memory482, which may set the transmit power, periodicity of the PRACHtransmissions, duration, and the like. The individual settings stored inPRACH setting 1503 may be predetermined by the network, the equipmentmanufacturer, or may be included in the trigger signal received from theserving base station. Once the PRACH signals are generated, UE 600transmits the signals over wireless radios 1500.

FIG. 10 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure. At block1000, a DPN enters a reduced power mode. With reference to FIG. 16, ablock diagram of a DPN 601 is illustrated configured according to oneaspect of the present disclosure. In example of the blocks presented inFIG. 10, DPN 601 includes a controller/processor 440 which executeslogic stored in memory 442 and controls components that define thefeatures and functionality of DPN 601. DPN 601 further includes wirelessradios 1600, signal detector 1601, and power controller 1602. Wirelessradios 1600 may include individual components as illustrated further inFIG. 4. Signal detector 1601 may also include individual components,such as MIMO detector 436 and receive processor 438. When not fullyengaged in communication with served UEs, DPN 601, under control ofcontroller/processor 440 controlling power controller 1602, may reducepower to switch into a low-powered state.

At block 1001, the DPN monitors for PRACH transmissions from one or moreUEs proximate to the DPN. For example, controller/processor 440 executesPRACH-based proximity logic 1603 in memory 442 to begin monitoring forany PRACH transmissions from proximate UEs received through wirelessradios 1600.

At block 1002, the DPN detects a plurality of candidate PRACHtransmissions. For example, signals that are received at DPN 601 throughwireless radios 1600 are processed through signal detector 1601, undercontrol of controller/processor 440 executing PRACH-based proximitylogic 1603, to determine whether such received signals are PRACHtransmissions.

At block 1003, the DPN combines the plurality of candidate PRACHtransmissions to determine a detected PRACH transmission from a UE. Forexample, with transmission by proximate UEs of periodic or multiplePRACH signals, DPN 601, with signal detector 1601 under control ofcontroller/processor 440, may use statistical combining of the multiplecandidate PRACH signals received via wireless radios 1600 to moreaccurately determine whether the candidate PRACH signals are, indeed,detected PRACH signals.

At block 1004, the DPN determines a proximity of the UE based on thedetected PRACH transmission. For example, under control ofcontroller/processor 440 executing PRACH-based proximity logic 1603, thedistance of the UE transmitting the detected PRACH signals may bedetermined by comparing the received signal power of the PRACH signalwith the known or estimated transmit power by the UE. If the determineddistance falls with a threshold distance from DPN 601,controller/processor 440 determines the UE to be proximate to DPN 601.

At block 1005, the DPN modifies operation of the DPN in response to theproximity. For example, when DPN 601 determines that the UE transmittingthe detected PRACH signals is proximate, controller/processor 440 maycause power controller 1602 to switch DPN 601 from the low-powered stateinto a fully-powered state. In the fully-powered state, DPN 601 mayprepare for handover of the UE from its current serving base station ormay provide carrier support in a carrier aggregation application.

FIG. 11 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure. At block1100, a serving base station receives a PRACH transmission from a mobiledevice. In example of the blocks presented in FIG. 11, wireless radios1400 of eNB 602 may also include individual components, such as MIMOdetector 436, in addition to the components noted with regard to FIG. 8.Signals received through wireless radio 1400 are decoded andinterpreted, under control of controller/processor 440 as PRACHtransmissions from a proximate UE. The combination of these componentsand acts may provide means for receiving, at a serving base station, aPRACH transmission from a mobile device.

At block 1101, the serving base station delays transmission of a PRACHacknowledgement message to the mobile device. For example, in executionby controller/processor 440 of PRACH-based proximity logic 1402, theexecuting operations cause eNB 602 to delay transmitting theacknowledgement message (e.g., msg2) to the UE transmitting the PRACHsignals. The delay may be implemented using a timer (not shown) or bymeasuring the receive power of the PRACH transmissions and triggeringtransmission of the acknowledgement when the receive power correspondsto a full power transmission from the UE. The combination of thesecomponents and acts may provide means for delaying, by the serving basestation, transmission of a PRACH acknowledgement message to the mobiledevice.

In various aspects of the disclosure, thresholds may be staticallyconfigured, semi-statically-configured, such as through the operations,administration, maintenance (OAM) interface, or the thresholds may bedynamically maintained or optimized based on various conditions, such asdownlink measurements (e.g., by a UeNB, such as UeNB 703), networkevents, or network listening. Dynamic optimization may be used toaddress issues, such as false alarms, where, after detecting proximityto a UE, powering up, but not experiencing a handover or instruction toprovide carrier support. If such false alarms are experienced for aparticular base station, the DPN may optimize the threshold associatedwith that base station by increasing the threshold. Thresholds may alsobe optimized based on current loading conditions, both of the basestations in the neighbor list and of the particular DPN. If the basestations signal a high loading, the DPN may reduce the threshold inorder to increase the availability for alleviating the base stationload. If the DPN has a higher loading, then the threshold may beincreased, in order to avoid further loading through handover ofproximate UEs.

FIG. 12 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure. At block1200, a DPN enters a reduced power mode at a DPN. In example of theblocks presented in FIG. 10, DPN 601 includes a controller/processor 440which executes logic stored in memory 442 and controls components thatdefine the features and functionality of DPN 601. DPN 601 furtherincludes wireless radios 1600, signal detector 1601, and powercontroller 1602. Wireless radios 1600 may include individual componentsas illustrated further in FIG. 4, such as TX MIMO processor 430,modulator/demodulators 432 a-t, and antennas 434 a-t. Signal detector1601 may also include individual components, such as MIMO detector 436and receive processor 438. When not fully engaged in communication withserved UEs, DPN 601, under control of controller/processor 440controlling power controller 1602, may reduce power to switch into alow-powered state. The combination of these components and acts mayprovide means for entering a reduced power mode at a DPN.

At block 1201, the DPN monitors for a set of root sequences associatedwith at least one base station in a neighbor list that it maintains. Forexample, DPN 601 maintains neighbor list 1604 in memory 442. Theneighbor list 1604 may be autonomously compiled and maintained by DPN601 using measurements and network listening or maybe staticallyconfigured by the network or equipment manufacturer or semi-staticallyconfigured through the network. Each base station in neighbor list 1604is distinguished based on the set root sequences that may be sent in aPRACH transmission. Through execution of PRACH-based proximity logic1603 by controller/processor 440, signal detector 1601 is configured tomonitor for the set of root sequences that are embedded in the detectedPRACH transmissions received through wireless radios 1600. Thecombination of these components and acts may provide means formonitoring, by the DPN, for a set of root sequences associated with atleast one base station in a neighbor list at the DPN, wherein the set ofroot sequences are located in PRACH transmissions from one or more UEs.

At block 1202, the DPN determines a proximity of a UE based on a receivepower of the PRACH transmission. For example, under control ofcontroller/processor 440 executing PRACH-based proximity logic 1603, thedistance of the UE transmitting the detected PRACH signals may bedetermined by comparing the received signal power of the PRACH signalwith the known or estimated transmit power by the UE. If the determineddistance falls with a threshold distance from DPN 601,controller/processor 440 determines the UE to be proximate to DPN 601.The combination of these components and acts may provide means fordetermining, by the DPN, a proximity of a UE based on a receive power ofthe PRACH transmission associated with a detected set of root sequencesassociated with one of the at least one base station in the neighborlist.

At block 1203, the DPN modifies operation of the DPN in response to theproximity. For example, when DPN 601 determines that the UE transmittingthe detected PRACH signals is proximate, controller/processor 440 maycause power controller 1602 to switch DPN 601 from the low-powered stateinto a fully-powered state. In the fully-powered state, DPN 601 mayprepare for handover of the UE from its current serving base station ormay provide carrier support in a carrier aggregation application. Thecombination of these components and acts may provide means for modifyingoperation of the DPN in response to the proximity.

FIG. 13 is a functional block diagram illustrating example blocksexecuted to implement one aspect of the present disclosure. At block1300, a DPN compares the receive power with a threshold associated toone of the base stations in the neighbor list to which the PRACHtransmission is sent by the UE. For example, in addition to the basestations that are identified in neighbor list 1604, each such basestation in neighbor list 1604 may be assigned a threshold value insignal thresholds 1605. The threshold values are assigned based onvarious characteristics and conditions, such as propagation conditions,geographic features, antenna configurations, and the like. Thethresholds in signal thresholds 1605 are used by DPN 601 under controlof controller/processor 440 in determining proximity of the UEtransmitting the detected PRACH signals. The combination of thesecomponents and acts may provide means for comparing the receive powerwith a threshold associated to the one of the at least one base stationin the neighbor list to which the PRACH transmission is sent by the UE,wherein each of the at least one base station in the neighbor list isassociated with its own threshold.

At block 1301, a determination is made by the DPN whether the thresholdhas been exceeded. For example, in executing PRACH-based proximity logic1603, controller/processor 440 compares the receive power of thedetected PRACH transmission with the specific threshold maintained insignal thresholds 1605 that is associated with the base station inneighbor list 1604 to which the UE is transmitting the PRACH signal.

At block 1302, if the threshold is not met, the DPN determines that theUE is not proximate to the DPN. For example, DPN 601 may determine thatthe threshold has not been met and remain in its low-powered state.

At block 1303, if the threshold is met, the DPN will indicate that theUE is proximate to the DPN. For example, DPN 601 may determine that thethreshold is met and trigger power controller 1602, under control ofcontroller/processor 440, to reestablish full power.

It should be noted that where A2 thresholds (where the serving celldrops below a specific serving threshold) are configured for determiningwhether a base station should begin sending PRACH orders to a given UE,the A2 thresholds and PRACH power thresholds may be jointly optimized asdescribed above. Moreover, A2 events, different thresholds, and othervarious related configurations may be exchanged among the base stationsusing the backhaul network.

In various further aspects of the present disclosure, neighbor-specificPRACH configurations may be provided for serving cell determination.This process involves identifying which base station in the neighborlist the UE sending PRACH is associated to. For example, referring backto wireless network 70 of FIG. 7, when a DPN, such as DPN 702 or UeNB703, detects the PRACH signals 705, it may not readily know whether UE701 is associated with serving eNB 700, eNBs 706-707, or access node708. Because the thresholds are associate with particular base stationsin the neighbor list, the DPN would desire to identify the particularbase station in order to apply the appropriate threshold. Thisidentification can be obtained in various aspects by means of suitablepartitioning of PRACH resources (e.g., preambles or transmission timeopportunities) among the neighbor eNBs. Depending, for example, on whenthe preamble is received, or which preamble is received, the DPN, suchas DPN 702 or UeNB 703, determines which of the base stations is theserving base station and applies the corresponding threshold. Forexample, if UeNB 703 detects PRACH signal 710, UeNB 703 may use thePRACH resource partitioning to determine that eNB 706 is the servingbase station. UeNB 703 would then apply the threshold associated witheNB 706 in its neighbor list.

It should be noted that configuration of the PRACH resourcepartitioning, such as with non-colliding PRACH resources, preamble IDs,timing, and the like, macro base stations may coordinate using thebackhaul network. Such coordination may be dynamic or semi-static, suchas through exchanging configurations.

In some instances, a DPN may encounter a negative delay, for instancewhen the UE is closer to the DPN than to its serving eNB. In this case,the cyclic shift of a detected PRACH signal does not match up with theexpected shift based on the expected location of the UE or serving basestation. The DPN cannot accurately detect proximity with such a negativedelay. Therefore, in order to accommodate such instances, the DPNmonitors two consecutive PRACH cyclic shifts. With the two consecutivecyclic shifts, the DPN may average the signal-to-interference-plus-noiseratio (SINR) resulting across the two shifts, take the maximum receivedenergy across the cyclic shifts, or the like in order to make thedetermination.

It should be noted that, for the transmitting side, in order to avoidambiguity, the base station should make sure that an adjacent shift isnot used when sending a PRACH order for neighbor cell proximitydetection.

It should further be noted that the timing estimates monitored by a DPNmay be used, in addition to received energy of the PRACH in order toreduce the number of false positives that could occur. For example,where the energy of the detected PRACH exceeds a particular threshold,yet the timing falls outside of a predefined window of what the expectedtiming should be, the DPN may determine not to fully activate. Such apredefined window may be determined based on the network deployment.

It should be noted that in additional aspects of the present disclosure,interference cancellation principles may be used to reduce interferencewhen multiple PRACH signals from multiple UEs occur on the sameresources. Estimated SINR will typically saturate at highcarrier-to-interference (C/I) because of energy leakage. Because of thisrelationship, it is possible to: (i) estimate the channel impulseresponse from the UE to the DPN, (ii) reconstruct the received signalcorresponding to the transmitted preamble, since both the sequence andthe channel are known or estimated, (iii) remove the re-constructedsignal from the received signal, and (iv) compute cross-correlation ofthe cleaned up received signal with an unused root sequence to computenoise. These steps are repeated for every detected sequence.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

The functional blocks and modules in FIGS. 8-13 may comprise processors,electronics devices, hardware devices, electronics components, logicalcircuits, memories, software codes, firmware codes, etc., or anycombination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure. Skilled artisans will also readilyrecognize that the order or combination of components, methods, orinteractions that are described herein are merely examples and that thecomponents, methods, or interactions of the various aspects of thepresent disclosure may be combined or performed in ways other than thoseillustrated and described herein.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. A computer-readable storage medium may be anyavailable media that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM orother optical disk storage, magnetic disk storage or other magneticstorage devices, or any other medium that can be used to carry or storedesired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, non-transitory connections may properly be includedwithin the definition of computer-readable medium. For example, if theinstructions are transmitted from a website, server, or other remotesource using a coaxial cable, fiber optic cable, twisted pair, ordigital subscriber line (DSL), then the coaxial cable, fiber opticcable, twisted pair, or DSL are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

The invention claimed is:
 1. A method of wireless communication,comprising: transmitting, from a serving base station, a signal to amobile device in communication with the serving base station, whereinthe signal triggers the mobile device to transmit periodic transmissionson a physical random access channel (PRACH) during a time period,wherein the mobile device remains in communication with the serving basestation and continues decoding data received from the serving basestation during the time period; transmitting, by the serving basestation, downlink data to the mobile device for decoding during the timeperiod; and receiving, by the serving base station, uplink data from themobile device during the time period, wherein the signal includes one ormore of: a signature sequence set for the periodic transmissions on thePRACH; a transmit power delta for open loop transmission power control;a fixed transmit power for the periodic transmissions on the PRACH; anda proximity detection flag.
 2. The method of claim 1, furthercomprising: transmitting, from the serving base station, a deactivationsignal to the mobile device, wherein the deactivation signal stops theperiodic transmissions on the PRACH during the time period.
 3. Themethod of claim 1, wherein the signal includes one or more of: aduration of the periodic transmissions on the PRACH; an interval of theperiodic transmissions on the PRACH; and a periodicity of the periodictransmissions on the PRACH.
 4. The method of claim 1, wherein the one ormore included in the signal further includes one or more of: a decodecontinuation signal, wherein the decode continuation signal signals themobile device to continue the decoding of the data received from theserving base station during the periodic transmissions on the PRACH; anda combination of the one or more included in the signal, wherein theproximity detection flag indicates to the mobile device to use one of: astandard transmit power and the fixed transmit power.
 5. The method ofclaim 4, wherein the fixed transmit power includes one of: apredetermined transmit power less than maximum transmit power of themobile device; and the maximum transmit power of the mobile device. 6.The method of claim 5, wherein the predetermined transmit power issignaled by a wireless communication network.
 7. The method of claim 1,further comprising: receiving, at the serving base station, a PRACHtransmission from the mobile device during the periodic transmissions onthe PRACH; and delaying, by the serving base station, transmission of aPRACH acknowledgement message to the mobile device.
 8. The method ofclaim 7, further comprising: detecting a preamble in the received PRACHassociated with the mobile device, wherein the delaying includes:delaying transmission of the PRACH acknowledgement for a predeterminedtime.
 9. An apparatus configured for wireless communication, comprising:at least one processor; and a memory coupled to the at least oneprocessor, wherein the at least one processor is configured: totransmit, from a serving base station, a signal to a mobile device incommunication with the serving base station, wherein the signal triggersthe mobile device to transmit periodic transmissions on a physicalrandom access channel (PRACH) during a time period, wherein the mobiledevice remains in communication with the serving base station andcontinues decoding data received from the serving base station duringthe time period; to transmit, by the serving base station, downlink datato the mobile device for decoding during the time period; and toreceive, by the serving base station, uplink data from the mobile deviceduring the time period, wherein the signal includes one or more of: asignature sequence set for the periodic transmissions on the PRACH; atransmit power delta for open loop transmission power control; a fixedtransmit power for the periodic transmissions on the PRACH; and aproximity detection flag.
 10. The apparatus of claim 9, furthercomprising configuration of the at least one processor to transmit, fromthe serving base station, a deactivation signal to the mobile device,wherein the deactivation signal stops the periodic transmissions on thePRACH during the time period.
 11. The apparatus of claim 9, wherein thesignal includes one or more of: a duration of the periodic transmissionson the PRACH; an interval of the periodic transmissions on the PRACH;and a periodicity of the periodic transmissions on the PRACH.
 12. Theapparatus of claim 9, wherein the one or more included in the signalfurther includes one or more of: a decode continuation signal, whereinthe decode continuation signal signals the mobile device to continue thedecoding of the data received from the serving base station during theperiodic transmissions on the PRACH; and a combination of the one ormore included in the signal, wherein the proximity detection flagindicates to the mobile device to use one of: a standard transmit powerand the fixed transmit power.
 13. The apparatus of claim 9, furthercomprising configuration of the at least one processor: to receive, atthe serving base station, a PRACH transmission from the mobile deviceduring the periodic transmissions on the PRACH; and to delay, by theserving base station, transmission of a PRACH acknowledgement message tothe mobile device.
 14. A non-transitory computer-readable medium havingprogram code recorded thereon, the program code comprising program codefor causing a computer: to transmit, from a serving base station, asignal to a mobile device in communication with the serving basestation, wherein the signal triggers the mobile device to transmitperiodic transmissions on a physical random access channel (PRACH)during a time period, wherein the mobile device remains in communicationwith the serving base station and continues decoding data received fromthe serving base station during the time period; to transmit, by theserving base station, downlink data to the mobile device for decodingduring the time period; and to receive, by the serving base station,uplink data from the mobile device during the time period, wherein thesignal includes one or more of: a signature sequence set for theperiodic transmissions on the PRACH; a transmit power delta for openloop transmission power control; a fixed transmit power for the periodictransmissions on the PRACH; and a proximity detection flag.
 15. Thenon-transitory computer-readable medium of claim 14, further comprising:program code for causing the computer to transmit, from the serving basestation, a deactivation signal to the mobile device, wherein thedeactivation signal stops the periodic transmissions on the PRACH duringthe time period.
 16. The non-transitory computer-readable medium ofclaim 14, wherein the signal includes one or more of: a duration of theperiodic transmissions on the PRACH; an interval of the periodictransmissions on the PRACH; and a periodicity of the periodictransmissions on the PRACH.
 17. The non-transitory computer-readablemedium of claim 14, wherein the one or more included in the signalfurther includes one or more of: a decode continuation signal, whereinthe decode continuation signal signals the mobile device to continue thedecoding of the data received from the serving base station during theperiodic transmissions on the PRACH; and a combination of the one ormore included in the signal, wherein the proximity detection flagindicates to the mobile device to use one of: a standard transmit powerand the fixed transmit power.
 18. The non-transitory computer-readablemedium of claim 17, wherein the fixed transmit power includes one of: apredetermined transmit power less than maximum transmit power of themobile device; and the maximum transmit power of the mobile device. 19.The non-transitory computer-readable medium of claim 18, wherein thepredetermined transmit power is signaled by a wireless communicationnetwork.
 20. The non-transitory computer-readable medium of claim 14,further comprising: program code for causing the computer to receive, atthe serving base station, a PRACH transmission from the mobile deviceduring the periodic transmissions on the PRACH; and program code forcausing the computer to delay, by the serving base station, transmissionof a PRACH acknowledgement message to the mobile device.
 21. Thenon-transitory computer-readable medium of claim 20, further comprising:program code for causing the computer to detect a preamble in thereceived PRACH associated with the mobile device, wherein the programcode for causing the computer to delay includes: program code forcausing the computer to delay transmission of the PRACH acknowledgementfor a predetermined time.
 22. An apparatus configured for wirelesscommunication, comprising: means for transmitting, from a serving basestation, a signal to a mobile device in communication with the servingbase station, wherein the signal triggers the mobile device to transmitperiodic transmissions on a physical random access channel (PRACH)during a time period, wherein the mobile device remains in communicationwith the serving base station and continues decoding data received fromthe serving base station during the time period; means for transmitting,by the serving base station, downlink data to the mobile device fordecoding during the time period; means for receiving, by the servingbase station, uplink data from the mobile device during the time period;and means for transmitting, from the serving base station, adeactivation signal to the mobile device, wherein the deactivationsignal stops the periodic transmissions on the PRACH during the timeperiod, wherein the signal includes one or more of: a signature sequenceset for the periodic transmissions on the PRACH; a transmit power deltafor open loop transmission power control; a fixed transmit power for theperiodic transmissions on the PRACH; and a proximity detection flag. 23.The apparatus of claim 22, wherein the signal further includes one ormore of: a duration of the periodic transmissions on the PRACH; aninterval of the periodic transmissions on the PRACH; a periodicity ofthe periodic transmissions on the PRACH; a decode continuation signal,wherein the decode continuation signal signals the mobile device tocontinue decoding data received from the serving base station during theperiodic transmissions on the PRACH; and a combination thereof, whereinthe proximity detection flag indicates to the mobile device to use oneof: a standard transmit power and the fixed transmit power.
 24. Theapparatus of claim 23, wherein the fixed transmit power includes one of:a predetermined transmit power less than maximum transmit power of themobile device; and the maximum transmit power of the mobile device. 25.The apparatus of claim 24, wherein the predetermined transmit power issignaled by a wireless communication network.
 26. The apparatus of claim22, further comprising: means for receiving, at the serving basestation, a PRACH transmission from the mobile device during the periodictransmissions on the PRACH; and means for delaying, by the serving basestation, transmission of a PRACH acknowledgement message to the mobiledevice.
 27. The apparatus of claim 26, further comprising: means fordetecting a preamble in the received PRACH associated with the mobiledevice, wherein the means for delaying includes: means for delayingtransmission of the PRACH acknowledgement for a predetermined time.